Additives for papermaking

ABSTRACT

The present invention provides systems and methods for papermaking. In embodiments, the systems include a first population of fibers dispersed in an aqueous solution and complexed with an activator, and a second population of composite additive particles bearing a tethering material, wherein the addition of the second population to the first population attaches the composite additive particles to the fibers by the interaction of the activator and the tethering material. Methods for forming a fibrous web are also disclosed, in addition to paper products formed from such fibrous webs.

RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US12/53098, which designated the United States and was filed on Aug.30, 2012, published in English, which claims the benefit of U.S.Provisional Application Ser. No. 61/530,260, filed Sep. 1, 2011 and U.S.Provisional Application Ser. No. 61/660,146, filed Jun. 15, 2012. Theentire contents of the above applications are incorporated by referenceherein.

FIELD OF THE APPLICATION

This application relates generally to making high-strength paperproducts with specific functionalities.

BACKGROUND

Many paper applications require not only high strength but alsofunctionalities that provide the paper article with moisture, oil andgrease, mold and fire resistance, increased brightness, or otherspecialized functionalities like antimicrobial properties or magneticproperties. Certain of these products are currently manufactured byimparting paper a coating in a secondary process.

In one approach for adding functionality to the paper surface, thesizing process uses cooked starch solutions with additives (such asbrightening agents, clays, hydrophobicizing compounds) to impart surfacefunctionality to the paper. In the sizing process, the wet web is firstdried to a pre-set moisture content and/or is re-wet to achieve uniformmoisture content throughout; then the material is fed into a size presswhere a high loading of gelatinized starch with additives is applied tothe paper surface; then the material is dried again. This processinvolves a number of downstream processes that can be inefficient.Inefficiencies result from the number of steps involved in preparing thesubstrate, cooking the starch and applying it to form the finishedproduct. A considerable amount of energy is required for these steps,which adds to the costs of the process.

For certain paper products, functionalities can be added byincorporating additives into the fibrous matrix during the papermakingprocess. Particulate additives can be introduced into the paper web,substituting for some of the pulp that might be used otherwise. Theseparticulate fillers can create, for example, a bulky final paper productthat creates the impression of higher quality through its tactileproperties while minimizing the use of expensive pulp. Particulatefillers can also be used to impart other specialized properties besidesbulk. For example, particulate additives can include filler particles,or other particles, suitable for use in papermaking, or a final paperproduct can include mineral particles such as calcium carbonate,dolomite, calcium sulfate, kaolin, talc, titanium dioxide, silica,aluminum hydroxide, and the like. Particles can be formed from inorganicor organic materials, and may be solid or porous. Organic particles maybe polymeric, optionally crosslinked, and may be elastomeric. A widevariety of particles known in the art can be incorporated into thefinished paper product to improve performance attributes such asbrightness, opacity, smoothness, ink receptivity, fire retardance, waterresistance, bulk, and the like.

Precipitated Calcium Carbonate (PCC) is particularly useful as aparticulate filler additive where high opacity, brightness andmaintenance of caliper are required. Higher PCC contents replaceexpensive pulp improving the profitability of paper. Although PCCcontents as high as 15% are often used in papermaking, the first passretention of the filler is poor, so that a significant amount can belost from the paper product during the papermaking process. The PCC thatis incorporated into the paper product also leads to weaker sheets,because the particles themselves disrupt the hydrogen bonding betweencellulose fibers. Higher ash content (>15%) is highly desired in thepaper industry, where ash content indicates the amount of filler in apaper.

In other products, TiO2 particles are highly desired as particulatefillers to improve the opacity and brightness beyond what is achievableusing PCC. The TiO2 particles due to their small size and highrefractive index are capable of scattering light and improving theopacity of the paper containing them. As the TiO2 particles are manytimes more expensive than PCC, improvement in retention is highlydesired. Although flocculants can be used to improve the retention ofTiO2, the flocculated TiO2 particles do not possess the same opticalproperties as the individual TiO2 platelets. It would be advantageous tocombine TiO2 particles with other particles to form a composite thatseparates individual TiO2 particles and allows them to retain theiroptical characteristics.

Other particulate fillers can be added to the paper product to impartspecific, desirable properties. As an example, magnetic or paramagneticparticles can be incorporated into the paper to form a magnetic or amagnetizable paper. As another example, colloidal silver particles canbe introduced into a paper product to impart antimicrobial properties. Alarge number of additives can be contemplated that are available inparticulate form, including additives that impart oil or greaseresistance, optical brightening, ink binding, dust control, waterrepellency, stiffness, biocidal properties, bioactive properties (e.g.,a biomolecule for controlled release), adhesive properties, diagnosticsensing, filtration assist, targeted capture/sequestration, and thelike. For particulate additives, proper distribution within the papermatrix is important. For particulate additives that are expensive,proper retention is also important. And with the addition of anyadditive, its impact on the strength, stiffness and bulk of the finalpaper product must be considered.

A variety of other additives can be used to impart desirable propertiesto paper products, but face some of the same challenges: retention,distribution and impact on paper quality. Some other additives usedpresently to impart various functionalities to paper include syntheticfibers (imparting strength and hydrophobicity and absorbencycharacteristics), latex colloids (imparting properties such ashydrophobicity, oil and grease resistance, mold resistance, fireretardancy, impact resistance) etc. These components have poor affinityto pulp fibers, though, owing to lack of functional groups capable ofinteracting with cellulose fibers. As an example, latex colloids areparticularly useful for imparting resilience, barrier properties, bulk,impact resistance, damping, and the like. Latex particles that aremicron or submicron sized (typically 100 nm particles) suspended in anaqueous solution are particularly suited for use in papermaking.However, latex is typically water-insoluble, and can be integrated onlywith great difficulty into an aqueous process like papermaking.

It is desirable, therefore, to have a process where an additive capableof delivering added functionality can be mixed with pulp fibers in thewet-end of papermaking such that the additive becomes an integral partof it. It is desirable that such additives be distributed evenly andappropriately within the paper matrix, and that the additives beretained on the product and not lost in the whitewater. It is furtherdesirable to introduce such additives so that they preserve the strengthand resiliency of the final paper product.

As an example, there exists a particular need in the art for systems andmethods that incorporate and retain colloidal latex particles in the wetend so that high amounts of these fillers are dispersed uniformly in thepaper providing paper with desired functionalities. These colloidallatex fillers should, desirably, be incorporated so that they are stablyanchored to the pulp fibers, allowing them to expand or gelatinizeduring paper manufacturing without being dislodged. In this manner, thefillers can occupy the interstitial spaces between cellulose fibers morecompletely, improving the properties of the paper product. Furthermore,it is known that high filler content has a detrimental effect on thestrength of the wet web before it is dried because the fillers act asspacers and interfere with fiber-fiber bonding. An efficient retentionsystem that attaches the latex fillers to fibers durably in the wet webcan advantageously enhance wet web strength during processing byallowing fiber-fiber bonding to proceed unimpeded.

SUMMARY

Disclosed herein in embodiments are systems for papermaking, comprisinga first population of fibers dispersed in an aqueous solution andcomplexed with an activator, and a second population of compositeadditive particles bearing a tethering material, wherein the addition ofthe second population to the first population attaches the compositeadditive particles to the fibers by the interaction of the activator andthe tethering material. The first population can comprise cellulosic orsynthetic fibers. The composite additive particles can comprise aparticle selected from the group of a PCC particle, a TiO2 particle, amagnetic particle, and a silver colloid particle. In embodiments, thecomposite additive particles comprise a latex component and a starchcomponent.

Further disclosed herein, in embodiments, are methods for manufacturinga paper product, comprising activating a first population of fibers in aliquid medium with an activator, forming a second population ofcomposite additive particles, treating the second population with atethering material to form tether-bearing composite additive particles,wherein the tethering material is capable of interacting with theactivator, adding the second population to the activated population offibers to form a treated paper matrix, and forming the paper matrix tomanufacture the paper product. In embodiments, the first populationcomprises cellulosic fibers or synthetic fibers. In embodiments, thecomposite additive particles comprise a particle selected from the groupof a PCC particle, a TiO2 particle, a magnetic particle, and a silvercolloid particle. In embodiments, the composite additive particlescomprise a latex component and a starch component.

Also disclosed herein, in embodiments, are methods for making a paperproduct, comprising providing a first population of fibers and a secondpopulation of fibers, wherein the fibers have low attachable affinityfor each other, activating the first population of fibers in a liquidmedium with an activator, treating the second population of fibers witha tethering material to form tether-bearing fibers, wherein thetethering material is capable of interacting with the activator, addingthe second population of tether-bearing fibers to the activatedpopulation of fibers to form a treated paper matrix, and forming thepaper matrix to manufacture the paper product. In embodiments, at leastone population of fibers comprises synthetic or cellulosic fibers. Inembodiments, one of the first population and the second populationcomprises hardwood fibers, and the other of the first population and thesecond population comprises softwood fibers.

Also disclosed, in embodiments, is a fibrous web, comprising a firstpopulation of fibers and a second population of fibers, wherein anactivator has been attached to the first population of fibers and atethering material has been attached to the second population of fibers,the tethering material interacting with the activator to attach thefirst population of fibers to the second population of fibers as afibrous web. Also disclosed, in embodiments, is a paper productcomprising the fibrous web as described above. In embodiments, the firstpopulation of fibers in the fibrous web comprises cellulosic fibers, andthe second population of fibers comprises synthetic fibers. Inembodiments, the first population of fibers consists essentially ofcellulosic fibers, and the second population of fibers consistsessentially of synthetic fibers. In embodiments, the first population offibers comprises one of softwood fibers or hardwood fibers, and thesecond population of fibers comprises the other of softwood and hardwoodfibers. In embodiments, the first population of fibers comprisescellulosic fibers, and the second population of fibers comprisesnon-cellulosic natural fibers. In embodiments, the first population offibers comprises one of softwood fibers or hardwood fibers, and thesecond population of fibers comprises the other of softwood and hardwoodfibers.

In addition, disclosed herein in embodiments are methods of forming afibrous web, comprising providing a first population of fibers,activating the first population of fibers in a liquid medium with anactivator, preparing a population of composite particles, wherein thecomposite particles comprise a latex component and a starch component,treating the population of composite particles with a tethering materialto form tether-bearing composite particles, wherein the tetheringmaterial is capable of interacting with the activator to attach thecomposite particles to the fibers to form particle-bearing fibers, andprocessing the particle-bearing fibers to gelatinize the starchcomponent and to melt the latex component, thereby distributing themelted latex component through the fibers and binding the fiberstogether to form the fibrous web. The method can further comprise thesteps of providing a second population of fibers, wherein the secondpopulation of fibers has low attachable affinity for the firstpopulation, activating the second population of fibers with anactivator, and adding the second population of fibers to the firstpopulation of fibers either before or after the activation step foreither population, wherein the population of tether-bearing compositeparticles attaches to the first population of fibers and the secondpopulation of fibers to form particle-bearing fibers, and wherein theprocessing of the particle-bearing fibers distributes the melted latexcomponent through the first population and the second population offibers and binds the first population and the second population offibers together to form the fibrous web. In embodiments, paper productsformed from the fibrous web described above are also disclosed.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 shows a photograph of samples of latex and cationic starch inwater.

FIG. 2 shows a graph of normalized load for pulp controls vs.experimental preparations.

FIG. 3 shows a table indicating hydrophobicity for various samples.

FIG. 4 shows a graph of normalized load for pulp controls vs.experimental preparations.

FIG. 5 shows a table indicating hydrophobicity for various samples.

FIG. 6 shows a graph of normalized load for pulp controls vs.experimental preparations.

FIG. 7 shows a table indicating hydrophobicity for various samples.

FIG. 8 shows a graph of normalized load for pulp plus additive controlsvs. experimental preparations.

DETAILED DESCRIPTION

1. Additives for Papermaking

Disclosed herein are systems and methods for attaching additives tocellulose fibers in a paper product. As used herein, the terms “paper”and “paper product” may be applied to a wide variety of sheet-likemasses, molded products, and other substrates fabricated from fibersderived from biological sources (e.g., fibrous cellulosic material),which may optionally include other fibrous elements derived from mineralsources (e.g., asbestos or glass) and/or from synthetic sources (e.g.,polyamides, polyesters, rayon and polyacrylic resins). As disclosedherein, a variety of specialized additives can be attached to the fibersin the paper product.

In embodiments, the additives are combined to form composite particles,and the composite particles are attached to the cellulose fibers.Composite particles can be formed by attaching two or more additives toeach other; the composite particles can then be attached to thecellulose fibers. Three steps can be performed to effect the attachmentof composite particle to cellulose fibers. In one step, the cellulosefibers are modified by the attachment of an agent, called an “activatingagent” or “activator” that prepares the surface of the fibers forattachment to a suitably-modified composite particle. In another step,the composite particle is formed as will be described in more detailbelow. The composite particle is then modified by attaching a tetheringagent to the particle, where the tethering agent has a particularaffinity for the activating agent attached to the paper fibers. Thetether-bearing composite additive particles are then admixed with theactivated fibers, so that the activating agent and the tethering agentsinteract: this interaction durably affixes the composite additiveparticles bearing the tethers to the fibers bearing the activators. Inembodiments, the cellulose fibers can be treated with a cationic polymerof a specific molecular weight and composition as an activator, and thecomposite additive particles are treated with an anionic polymer as atethering agent; these separately-treated populations are then combinedso that the composite additive particles are attached to the pulpfibers. In embodiments, the combination of these processes can bereferred to as an “Anchor-Tether-Activator,” or “ATA” system. In thissystem, the cellulose fibers are treated with the activator, as will bedescribed below in more detail; the composite additive particle acts asan “anchor particle” that is treated with the tethering agent. Thetether-bearing anchor particles, when mixed with the activated cellulosefibers, become attached thereto, so that the composite additiveparticles become durably affixed to the cellulose and appropriatelydistributed throughout the cellulose matrix.

In embodiments, the tethering agent also acts to attach the componentadditives to each other to form a composite additive particle. This useof the tethering agent can allow the creation of composite particlesfrom components that have no intrinsic attraction to each other. Forexample, PCC and TiO2 can be combined to form a composite additiveparticle using the tethering agent as “glue” to hold the componentstogether as a composite. Or, for example, TiO2 can be combined withanother additive, such as clay, to form a composite additive particle,using the tether as a “glue” to hold the composite together. Thecomposite additive particle, thus treated with the tethering agent,forms a tether-bearing composite particle that is affixable to theactivator-treated cellulose fibers in the anchor-tether-activator systemas described herein.

In embodiments, the components of the composite additive particle can beattached to each other intrinsically. In one embodiment, for example,starch granules and PCC particles can be mixed together physically toform a composite particle slurry. PCC is slightly cationic at the pHused for papermaking, which makes it easier to bond with anionic starchgranules. With neutral or uncharged starch granules, PCC can be mixed athigh shear to form a composite additive particle slurry that can then bemodified with tethering agent.

As another example, colloidal latex particles can interactelectrostatically with granular starch of opposite charge resulting in acomposite latex/starch additive particle. The composite latex-starchadditive particle can then be treated with a tethering agent asdescribed herein, and affixed to the activated cellulose fibers. Whenprepared and deployed in accordance with these systems and methods, sucha composite latex/starch additive can then used as functional additivewith appropriate chemistry to improve bonding and retention in the pulpin the wet-end of papermaking. In embodiments, the granular starchparticles can be used to deliver the latex into the papermaking web sothat they are distributed throughout the fibrous matrix. Attached to thestarch granules by electrostatic attraction, the latex particles thenbecome embedded uniformly in the fibrous web. As the starch granulesgelatinize during the papermaking process, they further spread theattached latex particles throughout the paper and onto the surface ofthe paper. These latex particles, depending on their melting orsoftening point, may then be advantageously incorporated in the finalpaper product, for example, forming a film in the paper during the paperdrying process or otherwise imparting desirable latex properties to thefinal paper product. In embodiments, starch granules encrusted withlatex (i.e., the composite latex/starch additive) helps to distributethe latex throughout the fibrous sheet via gelatinization and filmformation.

In embodiments, latex polymers are selected that are oppositely chargedfrom the starch granule that is selected to form the composite. Thus,latex/starch composites are formed and stabilized by electrostaticforces. As used herein, the term “latex” refers to a lyophobic colloidalsuspension of a synthetic polymer or a natural polymer (such ashydrocolloid particles of gums, methyl cellulose, CMC, and the like) ina liquid phase. The terms “latex polymer” or “latex particle” refer tothe polymeric material suspended in such a colloidal suspension. Latexcomprising synthetic polymers can be produced by a polymerizationreaction ex vivo. Examples of synthetic latex polymers or particlesinclude styrene-butadiene rubber, acrylonitrile butadiene styrene,acrylic polymers, polyvinyl acetate polymers, and the like.

For the uses as disclosed herein, a suitable latex can be chosen from awide variety of polymers. Some species of latex are inert polymers(Polyvinylacetate) while some are reactive (acrylic based), capable offlowing and crosslinking in the high temperature encountered in thedrying section of papermaking Latex can also be selected according tothe properties of its component polymers. For example, a useful latexcan be comprised of glassy polymers such as polystyrene when stiffnessis required, or rubbery polymers such as styrene-butadiene copolymers,when flexibility is required. In embodiments, a cationic latex is usedthat can be combined with a negatively charged starch particle.

Composite starch-latex additive particles as described herein can thenbe attached to the fibrous matrix formed by the papermaking process. Thecomposite starch-latex particles, however, lack strong affinity to thenatural and/or synthetic fibers used to form the paper web. Hence,additional steps as disclosed herein can be performed to attach thecomposite starch-latex particles to the fibrous web.

In embodiments, three steps as described previously can be performed toeffect this attachment. In one step, the fibers are modified by theattachment of an agent, called an “activating agent,” that prepares thesurface of the fibers for attachment to a suitably-modified compositestarch-latex particle. In another step, the starch-latex particle ismodified by attaching a tethering agent to the particle, where thetethering agent has a particular affinity for the activating agentattached to the paper fibers. The tether-bearing starch-latex particlesare then admixed with the activated fibers, so that the activating agentand the tethering agents interact: this interaction durably affixes thecomposite particles bearing the tethers to the fibers bearing theactivators. In embodiments, these systems and methods can be used totreat fibers used in papermaking with a cationic polymer of a specificmolecular weight and composition as an activator, to treat compositestarch-latex granules with an anionic polymer as a tethering agent, andto combine these separately treated populations so that the starchgranules are attached to the pulp fibers.

The present disclosure from time to time refers to fibers used inpapermaking as “pulp fibers.” It is recognized, though, that a varietyof fibers can be used in papermaking. As used herein, the term “fiber”can include natural fibers or synthetic fibers. Natural fibers caninclude fibers from animal sources (e.g., wool, hair, silk), fibers fromplant sources (e.g., cotton, flax, jute, cellulose), and fibers frommineral sources (e.g., asbestos, glass). As used herein, the term“natural fiber” refers to a fiber or a microfiber derived from a naturalsource without artificial modification. Natural fibers includevegetable-derived fibers, animal-derived fibers and mineral-derivedfibers. Vegetable-derived fibers can be predominately cellulosic, e.g.,cotton, jute, flax, hemp, sisal, ramie, and the like. Vegetable-derivedfibers can include fibers derived from seeds or seed cases, such ascotton or kapok. Vegetable-derived fibers can include fibers derivedfrom leaves, such as sisal and agave. Vegetable-derived fibers caninclude fibers derived from the skin or bast surrounding the stem of aplant, such as flax, jute, kenaf, hemp, ramie, rattan, soybean fibers,vine fibers, jute, kenaf, industrial hemp, ramie, rattan, soybean fiber,and banana fibers. Vegetable-derived fibers can include fibers derivedfrom the fruit of a plant, such as coconut fibers. Vegetable-derivedfibers can include fibers derived from the stalk of a plant, such aswheat, rice, barley, bamboo, and grass. Vegetable-derived fibers caninclude wood fibers. Animal-derived fibers typically comprise proteins,e.g., wool, silk, mohair, and the like. Animal-derived fibers can bederived from animal hair, e.g., sheep's wool, goat hair, alpaca hair,horse hair, etc. Animal-derived fibers can be derived from animal bodyparts, e.g., catgut, sinew, etc. Animal-derived fibers can be collectedfrom the dried saliva or other excretions of insects or their cocoons,e.g., silk obtained from silkworm cocoons. Animal-derived fibers can bederived from feathers of birds. Mineral-derived natural fibers areobtained from minerals. Mineral-derived fibers can be derived fromasbestos. Mineral-derived fibers can be a glass or ceramic fiber, e.g.,glass wool fibers, quartz fibers, aluminum oxide, silicon carbide, boroncarbide, and the like.

Synthetic fibers are fibers that are manufactured in whole or in part.Synthetic fibers include artificial fibers, where a natural precursorfiber is modified to form a fiber. Cellulose can also be modified toproduce cellulose acetate fibers, and can form artificial fibers such asRayon or Lyocell. In embodiments, artificial fibers can include fibersmade from cellulose substrates, for example cellulose esters (e.g.,cellulose acetate), rayon, bamboo fiber, lyocells, viscose rayon, andthe like. Synthetic fibers also include fibers made from non-naturalsources, can include fibers made from polyesters, aramids, acrylics,nylons, polyurethane, polyolefin, polyactides, and the like. Syntheticfibers can be formed from synthetic materials that are inorganic ororganic.

2. The Attachment Process

a. Activation

As used herein, the term “activation” refers to the interaction of anactivating material, such as a polymer, with suspended particles orfibers in a liquid medium, such as an aqueous solution. An “activator,”for example an “activator polymer,” can carry out this activation. Inembodiments, high molecular weight polymers can be introduced into theparticulate or fibrous dispersion as activator polymers, so that thesepolymers interact, or complex, with the dispersed particles or fibers.The polymer-fiber complexes interact with other similar complexes, orwith other fibers, and form agglomerates.

This “activation” step can function as a pretreatment to prepare thesurface of the suspended material (e.g., fibers) for furtherinteractions in the subsequent phases of the disclosed system andmethods. For example, the activation step can prepare the surface of thesuspended materials to interact with other polymers that have beenrationally designed to interact therewith in a subsequent “tethering”step, as described below. Not to be bound by theory, it is believed thatwhen the suspended materials (e.g., fibers) are coated by an activatingmaterial such as a polymer, these coated materials can adopt some of thesurface properties of the polymer or other coating. This altered surfacecharacter in itself can be advantageous for retention, attachment and/ordewatering.

In another embodiment, activation can be accomplished by chemicalmodification of the suspended material. For example, oxidants orbases/alkalis can increase the negative surface energy of fibers orparticles, and acids can decrease the negative surface energy or eveninduce a positive surface energy on suspended material. In anotherembodiment, electrochemical oxidation or reduction processes can be usedto affect the surface charge on the suspended materials. These chemicalmodifications can produce activated particulates that have a higheraffinity for tethered anchor particles as described below.

Suspended materials suitable for modification, or activation, caninclude organic or inorganic particles, or mixtures thereof. Inorganicparticles can include one or more materials such as calcium carbonate,dolomite, calcium sulfate, kaolin, talc, titanium dioxide, sand,diatomaceous earth, aluminum hydroxide, silica, other metal oxides andthe like.

Organic particles can include one or more materials such as starch,modified starch, polymeric spheres (both solid and hollow), carbon basednanoparticles such as carbon nanotubes and the like. Particle sizes canrange from a few nanometers to few hundred microns. In certainembodiments, macroscopic particles in the millimeter range may besuitable.

In embodiments, suspended materials may comprise materials such aslignocellulosic material, cellulosic material, minerals, vitreousmaterial, cementitious material, carbonaceous material, plastics,elastomeric materials, and the like. In embodiments, cellulosic andlignocellulosic materials may include wood materials such as woodflakes, wood fibers, wood waste material, wood powder, lignins, woodpulp, or fibers from woody plants.

The “activation” step may be performed using flocculants or otherpolymeric substances. Preferably, the polymers or flocculants can becharged, including anionic or cationic polymers.

In embodiments, anionic polymers can be used, including, for example,olefinic polymers, such as polymers made from polyacrylate,polymethacrylate, partially hydrolyzed polyacrylamide, and salts, estersand copolymers thereof such as (sodium acrylate/acrylamide) copolymers,sulfonated polymers, such as sulfonated polystyrene, and salts, estersand copolymers thereof. Suitable polycations include: polyvinylamines,polyallylamines, polydiallyldimethylammoniums (e.g., the chloride salt),branched or linear polyethyleneimine, crosslinked amines (includingepichlorohydrin/dimethylamine, and epichlorohydrin/alkylenediamines),quaternary ammonium substituted polymers, such as(acrylamide/dimethylaminoethylacrylate methyl chloride quat) copolymersand trimethylammoniummethylene-substituted polystyrene, and the like.Nonionic polymers suitable for hydrogen bonding interactions can includepolyethylene oxide, polypropylene oxide, polyhydroxyethylacrylate,polyhydroxyethylmethacrylate, and the like. In embodiments, an activatorsuch as polyethylene oxide can be used as an activator with a cationictethering material in accordance with the description of tetheringmaterials below. In embodiments, activator polymers with hydrophobicmodifications can be used. Flocculants such as those sold under thetrademark MAGNAFLOC® by Ciba Specialty Chemicals can be used.

In embodiments, activators such as polymers or copolymers containingcarboxylate, sulfonate, phosphonate, or hydroxamate groups can be used.These groups can be incorporated in the polymer as manufactured,alternatively they can be produced by neutralization of thecorresponding acid groups, or generated by hydrolysis of a precursorsuch as an ester, amide, anhydride, or nitrile group. The neutralizationor hydrolysis step could be done on site prior to the point of use, orit could occur in situ in the process stream.

The activated suspended material (e.g., fiber) can also be an aminefunctionalized or modified. As used herein, the term “modified material”can include any material that has been modified by the attachment of oneor more amine functional groups as described herein. The functionalgroup on the surface of the suspended material can be from modificationusing a multifunctional coupling agent or a polymer. The multifunctionalcoupling agent can be an amino silane coupling agent as an example.These molecules can bond to a material's surface and then present theiramine group for interaction with the particulate matter. In the case ofa polymer, the polymer on the surface of a suspended fiber or particlecan be covalently bound to the surface or interact with the surface ofthe particle and/or fiber using any number of other forces such aselectrostatic, hydrophobic, or hydrogen bonding interactions. In thecase that the polymer is covalently bound to the surface, amultifunctional coupling agent can be used such as a silane couplingagent. Suitable coupling agents include isocyano silanes and epoxysilanes as examples. A polyamine can then react with an isocyano silaneor epoxy silane for example. Polyamines include polyallyl amine,polyvinyl amine, chitosan, and polyethylenimine.

In embodiments, polyamines (polymers containing primary, secondary,tertiary, and/or quaternary amines) can also self-assemble onto thesurface of the suspended particles or fibers to functionalize themwithout the need of a coupling agent. For example, polyamines canself-assemble onto the surface of the particles or fibers throughelectrostatic interactions. They can also be precipitated onto thesurface in the case of chitosan for example. Since chitosan is solublein acidic aqueous conditions, it can be precipitated onto the surface ofsuspended material by adding a chitosan solution to the suspendedmaterial at a low pH and then raising the solution pH.

In embodiments, the amines or a majority of amines are charged. Somepolyamines, such as quarternary amines are fully charged regardless ofthe pH. Other amines can be charged or uncharged depending on theenvironment. The polyamines can be charged after addition onto thesuspended particles or fibers by treating them with an acid solution toprotonate the amines. In embodiments, the acid solution can benon-aqueous to prevent the polyamine from going back into solution inthe case where it is not covalently attached to the particle or fiber.

The polymers or particles can complex via forming one or more ionicbonds, covalent bonds, hydrogen bonding and combinations thereof, forexample. Ionic complexing is preferred.

To obtain activated suspended materials, the activator could beintroduced into a liquid medium through several different means. Forexample, a large mixing tank could be used to mix an activating materialwith fine particulate materials. Activated particles or fibers areproduced that can be treated with one or more subsequent steps ofattachment to tether-bearing anchor particles.

b. Tethering

As used herein, the term “tethering” refers to an interaction between anactivated suspended particle or fiber and an additive particle, hereintermed an anchor particle (as described below). The additive particle,for example, a composite additive particle, (“anchor particle”) can betreated or coated with a tethering material. The tethering material,such as a polymer, forms a complex or coating on the surface of theanchor particles such that the tethered anchor particles have anaffinity for the activated suspended material. In embodiments, theselection of tether and activator materials is intended to make the twosolids streams complementary so that the activated particles or fibersin the suspension become tethered, linked or otherwise attached to theanchor particle.

In accordance with these systems and methods, the tethering materialacts as a complexing agent to affix the activated particles or fibers tothe additive particle anchor material. In embodiments, a tetheringmaterial can be any type of material that interacts strongly with theactivating material and that is connectable to an anchor particle.Composite latex-starch particles are an example of an additive particleor anchor particle that can be treated with a tethering agent.

In embodiments, various interactions such as electrostatic, hydrogenbonding or hydrophobic behavior can be used to affix an activatedcomplex to a tethering material complexed with an anchor particle.

For use in papermaking, an anchor particle can be selected from anyparticulate matter that is desirably attached to cellulose fibers in thefinal paper product. The tether-bearing anchor particle comprising thedesirable additive can then interact with the activated cellulose fibersin the wet paper stream. As an example, starch granules can be used asan anchor particle to be attached to the cellulose fibers, as isdescribed in more detail below. Or, as described herein, compositelatex-starch granules can be used as anchor particles, to be attachedvia tethering agents to activated fibers.

In embodiments, polymers such as linear or branched polyethyleneiminecan be used as tethering materials. It would be understood that otheranionic or cationic polymers could be used as tethering agents, forexample polydiallyldimethylammonium chloride (poly(DADMAC)). In otherembodiments, cationic tethering agents such as epichlorohydrindimethylamine (epi/DMA), styrene maleic anhydride imide (SMAI),polyethylene imide (PEI), polyvinylamine, polyallylamine, amine-aldehydecondensates, poly(dimethylaminoethyl acrylate methyl chloridequaternary) polymers and the like can be used. Advantageously, cationicpolymers useful as tethering agents can include quaternary ammonium orphosphonium groups. Advantageously, polymers with quaternary ammoniumgroups such as poly(DADMAC) or epi/DMA can be used as tethering agents.In other embodiments, polyvalent metal salts (e.g., calcium, magnesium,aluminum, iron salts, and the like) can be used as tethering agents. Inother embodiments cationic surfactants such asdimethyldialkyl(C8-C22)ammonium halides, alkyl(C8-C22)trimethylammoniumhalides, alkyl(C8-C22)dimethylbenzylammonium halides, cetyl pyridiniumchloride, fatty amines, protonated or quaternized fatty amines, fattyamides and alkyl phosphonium compounds can be used as tethering agents.In embodiments, polymers having hydrophobic modifications can be used astethering agents.

The efficacy of a tethering material, however, can depend on theactivating material. A high affinity between the tethering material andthe activating material can lead to a strong and/or rapid interactionthere between. A suitable choice for tether material is one that canremain bound to the anchor surface, but can impart surface propertiesthat are beneficial to a strong complex formation with the activatorpolymer. For example, a polyanionic activator can be matched with apolycationic tether material or a polycationic activator can be matchedwith a polyanionic tether material. In one embodiment, a poly(sodiumacrylate-co-acrylamide) activator is matched with a chitosan tethermaterial.

In hydrogen bonding terms, a hydrogen bond donor should be used inconjunction with a hydrogen bond acceptor. In embodiments, the tethermaterial can be complementary to the chosen activator, and bothmaterials can possess a strong affinity to their respective depositionsurfaces while retaining this surface property.

In other embodiments, cationic-anionic interactions can be arrangedbetween activated suspended materials and tether-bearing anchorparticles. The activator may be a cationic or an anionic material, aslong as it has an affinity for the suspended material to which itattaches. The complementary tethering material can be selected to haveaffinity for the specific anchor particles being used in the system. Inother embodiments, hydrophobic interactions can be employed in theactivation-tethering system.

3. Retention and Incorporation in Papermaking

It is envisioned that the complexes formed from the additive orcomposite additive (“anchor”) particles and the activated fibrous mattercan form a homogeneous part of a fibrous product like paper. Inembodiments, the interactions between the activated suspended fibers andthe tether-bearing anchor particles can enhance the mechanicalproperties of the complex that they form. For example, an activatedsuspended material can be durably bound to one or more tether-bearinganchor particles, so that the tether-bearing anchor particles do notsegregate or move from their position on the fibers. Increasedcompatibility of the activated fine materials with a denser (anchor)matrix modified with the appropriate tether polymer can lead to furthermechanical stability of the resulting composite material. For example,using latex-starch composites as tether-bearing anchor particles permitsthe latex to attach durably to the paper fibers; the gelatinization ofthe starch combined with the melting of the latex allows the flowablelatex to permeate the paper fibers and impart desirable propertiesthereto. In embodiments, the latex-starch composites can be attached tofibers having low or no attachable affinity for each other, such ascellulosic fibers and synthetic fibers or two different populations ofsynthetic fibers, such that the melting of the latex allows the flowablelatex to attach the fibers to each other to form a fibrous composite. Inembodiments, such a fibrous composite may have further advantageousproperties based, for example, on the elastomeric nature of the latexagent binding the fibers together. In other embodiments, theactivation-tethering system disclosed herein can be applied to attachdissimilar types of cellulose fibers together, such as softwood fibersand hardwood fibers.

Most papers and paperboards attain specific physical characteristics byusing a mixture of hardwood and softwood. Hardwood fibers are short inlength, typically around 1 mm and with a diameter of around 20 um,resulting in a length to diameter ratio of 50:1. Softwood fibers arelonger than hardwood, typically around 3 mm in length with a diameter of30 um, resulting in a length to diameter ratio of 100:1. Softwood fibersoffer high strength because of their ability to overlap and intertwine.Hardwood fibers offer good formation and improve aesthetics of the papersurface due to their small size. For a functional paper it is necessaryto have adequate wet strength when it is made such that it does notbreak on the web and have sufficient mechanical properties (such astensile and burst) that it could be used in its intended application(printing, photocopying for office pares and edge crush strength,stiffness and bulk for packaging applications). These mechanicalproperties are realized when the hardwood and softwood fibers areintimately mixed together and there is sufficient hydrogen bondingbetween them to enable strength and stiffness. To improve the low numberof hydrogen bonds between the fibers, it is necessary to increaseproximity of fibers and the number of contact points between them.

To achieve this, softwood fibers are subjected to refining processesthat enhance their surface area, induces fibrillation and overallimproves the contact area between hardwood and softwood fibers. Refiningcrushes the lumens of softwood cellulose fibers, changing them from acylindrical shape into a ribbon shape. There are several benefits torefining: the flat fibers result in a flatter paper surface; the fibrilscreated from refining result in more sites for hydrogen bonding; theratio of softwood and hardwood can be variably adjusted as necessarybecause of the increase in hydrogen bonding and good bond formation.Without refining, softwood fibers have a low attachable affinity tohardwood fibers. Refining, by increasing the surface area available forhydrogen bonding in the softwood fibers, improves the attachableaffinity of softwood fibers to hardwood fibers so that they can beattached to each other to form functional paper products.

But refining also creates problems: the increased hydrogen bondingcauses poor drainage on the paper machine; the additional residence timein a refiner is costly; the crushed lumen results in a significantdecrease in caliper per basis weight. Thus there exists a need toimprove the bonding between hardwood and softwood fibers withoutemploying the refining process, or with less intensive refining.Techniques as disclosed herein, described in more detail below, canattach the dissimilar hardwood and softwood fibers to each other withoutrefining, thereby decreasing or eliminating the exposure of the fibersto the refining process.

Hardwood fibers and unrefined softwood fibers are examples of dissimilarfibers having low attachable affinity to each other. In embodiments,other fibers dissimilar to cellulosic fibers can be introduced into thepaper product to improve functionalities and attain certain features.Certain of these dissimilar fibers can have a low attachable affinityfor the cellulosic fibers, such that the fibers do not coalesce duringpapermaking to make a functional paper product (i.e., one havingadequate wet strength when it is made such that it does not break on theweb and having sufficient mechanical properties (e.g., tensile and burststrength) allowing it to be used its intended application). Examples ofdissimilar fibers having a low attachable affinity to cellulosic fiberscan include vegetable stalk fibers, bast fibers and seed hull fibers.Vegetable stalk fibers such as sugarcane, bamboo, cereal straw (wheat,rye, oats, barley, rice), switchgrass, papyrus, corn, cotton, andsorghum have length to diameter ratios similar to softwood or hardwood,but often with high variation and have a high proportion of thin-walledcells. Bast fibers such as hemp, jute, kenaf, and flax are significantlymore robust than stalk fibers but still have a high variation of lengthand diameter. Vegetable stalk and bast fibers are relatively inexpensiveand most require only a year to reach full maturity (compared to woodwhich is in the range of 15-50 years). Economically, it would beadvantageous to use vegetable stalk and bast fibers as fillers incombination with cellulosic fibers to form paper products. Use of thesystems and methods disclosed herein can allow these fibers (e.g.,vegetable stalk and bast fibers) having low attachable affinity to beformed into paper products with cellulosic fibers. As used herein, theterm “low attachable affinity” also applies to fibers that have noattachable affinity to each other.

Dissimilar populations of fibers, such as a population of hardwoodfibers and a population of softwood fibers, or a population ofcellulosic fibers and a population of non-cellulosic (natural orsynthetic) fibers can be attached to each other by treating onepopulation with an activator, and the other population with a tetheringagent, and combining the two treated populations. Dissimilar fiberswhere the native attachment of one fiber population to the other fiberpopulation does not allow the two populations to coalesce duringpapermaking to make a functional paper product (i.e., one havingadequate wet strength when it is made such that it does not break on theweb and having sufficient mechanical properties (e.g., tensile and burststrength) allowing it to be used its intended application) areconsidered to be fiber populations having low attachable affinity. Atthe low end of the attachable affinity continuum are those fibers, suchas cellulosic and hydrophobic synthetic fibers (e.g., olefinic,polyamide, polyester fibers, and the like) that have minimal or noattachable affinity for each other.

The interaction of the activator and the tethering agent forms a durablecomplex binding the two dissimilar fiber populations together,overcoming the tendency of fiber populations with low attachableaffinity to form inadequate paper products, and reinforcing theattachment of fiber populations with a higher attachable affinity toeach other. In an exemplary embodiment of two populations of dissimilarfibers with low attachable affinity, hardwood fibers can be treated witha tethering agent and softwood fibers can be treated with an activator,or vice versa. Using the activator-tether system in this way can savethe time, energy and expense associated with processing the softwoodfibers as is currently done. These two treated populations can becombined to form a paper product, attaching the hardwood and thesoftwood fibers together without the need to subject the softwood fibersto the refining process. Similarly, cellulosic fibers can be treatedwith an activator, and hydrophobic synthetic fibers can be treated witha tethering agent or vice versa: this represents another example of twodissimilar fiber populations having low or no attachable affinity toeach other.

These two treated populations of dissimilar fibers can be combined toform a paper product, attaching (for example) the cellulosic and thenon-cellulosic fibers together to form a paper product havingspecialized properties. As an example, cotton seed hull fibers (bothstaple and linter) are significantly longer than softwood fibers withrelatively low variability in length and diameter, and can offer highstrength to specialty papers (i.e. currency), but are very expensive.Hull fibers, typically high in lignin and/or inorganic content aredissimilar to cellulose, and they represent low affinity attachablefibers. Their attachment to cellulosic fibers can be improved by usingthe systems and methods disclosed herein, allowing fewer of these fibersto be used for forming a high performance product. Advantageously, hullfibers can be used as high performance additives, in combination withcellulosic fibers to form paper products.

For papermaking, cationic and anionic polymers for activators andtethering agents (respectively) can be selected from a wide variety ofavailable polymers, as described above. In embodiments, starch granulesused to form starch-latex composites can be used in their native state,or they can be modified with short amine side-groups, with aminepolymers, or with hydrophobic side groups (each a “modified starch”).The presence of amines on the surface of the starch granules can help inattaching an anionic tethering polymer.

For activating the cellulose fibers, cationic polymers can be used. Thepolycation can be linked to the fiber surface using a coupling agent,for example a bifunctional crosslinking agent such as acarbonyldiimidazole or a silane, or the polyamine can self-assemble ontothe surface of the cellulose fiber through electrostatic, hydrogenbonding, or hydrophobic interactions. In embodiments, the polyamine canspontaneously self-assemble onto the fiber surface or it can beprecipitated onto the surface. For example, in embodiments, chitosan canbe precipitated on the surface of the cellulose fibers to activate them.Because chitosan is soluble only in an acidic solution, it can be addedto a cellulose fiber dispersion at an acidic pH, and then can beprecipitated onto the surface of the cellulose fibers by slowly addingbase to the dispersion until chitosan is no longer soluble. Inembodiments, a difunctional crosslinking agent can be used to attach thepolycation to the fiber, by reacting with both the polycation and thefiber.

In other embodiments, a polycation such as a polyamine can be addeddirectly to the fiber dispersion or slurry. For example, the additionlevel of the polycation can be between about 0.01% to 5.0% (based on theweight of the fiber), e.g., between 0.1% to 2%. For example, if thecellulose fiber population is treated with a polyamine likepoly(DADMAC), a separately treated population of tether-bearing starchgranules can be mixed in thereafter, resulting in the attachment of thestarch-latex composites to the cellulose fibers by the interaction ofthe activator polymer and the tether polymer. In embodiments,starch-latex composites can be treated with a variety of anionicpolymers, such as anionic polyacrylamide, which then act as tethers.

Starch that is to be treated in accordance with these systems andmethods can be further derivatized or coated with moieties that impartdesirable properties, e.g., hydrophobicity, oleophobicity or both.Starches thus modified may be also termed “modified starches.” Preferredoil resistant coating formulations are aqueous solutions of cellulosederivatives such as methylcellulose, ethyl cellulose, propyl cellulose,hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose,ethylhydroxypropyl cellulose, and ethylhydroxyethyl cellulose, celluloseacetate butyrate, which may further comprise polyvinyl alcohol and/orits derivatives. Another group of preferred oil resistant coatingcompositions are latex emulsions such as the emulsions of polystyrene,styrene-acrylonitrile copolymer, carboxylated styrene-butadienecopolymer, ethylene-vinyl chloride copolymer, styrene-acrylic copolymer,polyvinyl acetate, ethylene-vinyl acetate copolymer, and vinylacetate-acrylic copolymer. The starch granule thus coated with greaseresistant formulations could be attached to the activated pulp fibersvia tethering, such that the surface segregation of the starch granulewill modify the surface of the paper product.

In embodiments, the presence of hydrophobic starch also improves thehydrophobicity of the resulting paper without needing an internal sizingsuch as alkyl succinic anhydride (ASA), alkyl ketene dimer (AKD) orRosin. The gelatinized hydrophobic starch sizes the entire thickness ofthe paper. This property is useful in reducing the coating requirementsin making coated sheets. The coating applied using a roller or ametering bar or any such methods, would remain on the surface of thepaper and not impregnate the bulk of the paper thus needing less coatingto achieve the same amount of gloss and surface finish.

In other embodiments, the addition of a coating agent to the starch canimprove its mechanical properties such as bending stiffness or tensilestrength, or could improve its optical properties (e.g., TiO2nanoparticles bound to starch).

EXAMPLES

Materials

-   -   Market softwood and hardwood pulp    -   Recycled brown pulp    -   Unrefined softwood and hardwood pulp    -   Poly(diallyldimethylammonium chloride), Hi Molecular Weight, 20        wt % in water (polyDADMAC), Sigma-Aldrich, St. Louis, Mo.    -   MagnaFloc 919, Ciba Specialty Chemicals Corporation, Suffolk,        Va.    -   STA-LOK 300 Starch, Tate & Lyle, Decatur, Ill. (cationic starch)    -   COSEAL 30061A Anionic Latex, Rohm & Haas, Philedelphia, Pa.    -   ChitoClear Chitosan CG-10, Primex, Siglufjordur, Iceland    -   Polyethylene fibers PEFYB-00620, MiniFibers, Inc., Johnson City,        Tenn.    -   Modified Polyethylene fibers PEFYB-ONL490, MiniFibers, Inc.,        Johnson City, Tenn.    -   Polypropylene fibers (“PP”), PEFYB-00Y600, MiniFibers, Inc.,        Johnson City, Tenn.    -   PES/Nylon pie wedge bicomponent cut fibers    -   Precipitated Calcium Carbonate (PCC), Sigma-Aldrich, St. Louis,        Mo.    -   Douglas Pearl Starch (unmodified corn starch), Penford Products,        Cedar Rapids, Iowa    -   Iron (III) Oxide, <5 um, 99.9%, Sigma-Aldrich, St. Louis, Mo.

Example 1 Control Virgin Pulp

A 0.5% slurry was prepared by blending 3.5% by weight softwood andhardwood pulp mixture (in the ratio of 20:80) in water.

Example 2 Control Recycled Pulp

A 0.5% slurry was prepared by blending 22.5% recycled brown pulp inwater.

Example 3 Handsheet Preparation

Handsheets were prepared using a Mark V Dynamic Paper Chemistry Jar andHandSheet Mold from Paper Chemistry Laboratory, Inc. (Larchmont, N.Y.).Handsheets were prepared without addition of polymers as controls, usingthe pulps prepared as described in Example 1 and 2. Handsheets wereprepared with the addition of polymers as experimental samples, asdescribed below.

For preparing each experimental handsheet, the appropriate volume of0.5% pulp slurry prepared in accordance with Examples 1 or 2 (asapplicable) was activated with up to 2% of the selected polymer(s)(based on dry weight), as described below in more detail. Polymeradditions were performed at 5 minute intervals. This polymer-containingslurry was diluted with up to 3 L of water and added to the handsheetmaker, where it was mixed at a rate of 1100 RPM for 5 seconds, 700 RPMfor 5 seconds, and 400 RPM for 5 seconds. The water was then drainedoff. The subsequent sheet was then transferred off of the wire, pressedand dried.

For preparing sheets containing low melting point synthetic fibersPEFYB-00620, PEFYB-ONL490, PEFYB-00Y600, as described below in Example9, the sheets were dried as described above and then heated further toensure melting of the synthetic fibers.

Example 4 Tensile Test

Tensile tests were conducted on control and experimental samples usingan Instron 3343. Samples of handsheets for tensile testing wereinitially cut into 1 in wide strips with a paper cutter, and thenattached within the Instron 3343. The gauge length region was set at 4in and the crosshead speed was 1 in/minute. Thickness was measured toprovide stress data as was the weight to be able to normalize the databy weight of samples. The strips were tested to failure with anappropriate load cell. At least three strips from each control orexperimental handsheet sample were tested and the values were averagedtogether.

Example 5 Preparation of Latex-Coated Starch without Tether

StaLok 300 cationic starch was dispersed in water in slurry form suchthat the solids content was about 20%. COSEAL 30061A anionic latex wasadded to the cationic starch, up to 50% by weight of starch. The latexis spontaneously self-assembled on the starch surface resulting in aclear solution when the starch settles down. By contrast, the latexsolution without starch remains milky white, as shown in FIG. 1.

Example 6 Preparation Of Latex-Coated Starch With Tether

StaLok 300 cationic starch was dispersed in water in slurry form suchthat the solids content was about 20%. COSEAL 30061A anionic latex wasadded to the cationic starch, up to 50% by weight of starch.Latex-coated starch composite particles were formed, which acted as“anchor particles.” MagnaFloc 919 was then added 0.1% by weight as atethering agent.

Example 7 Process for Preparing Handsheets from Activated Pulp andLatex-Coated Starch (with and without Tether)

800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2(as applicable) was initially provided. The pulp slurry was activatedwith 0.1% by fiber weight polyDADMAC. Separately, latex-coated cationicstarch granules were prepared as a slurry in accordance with Example 5(i.e., a non-tether-bearing starch slurry), and tethered latex-coatedcationic starch granules were prepared as a slurry in accordance withExample 6 (i.e., a tether-bearing starch slurry). Each slurry was mixedfor 5 minutes individually and then the pulp slurry was combined with anon-tether-bearing or a tether-bearing starch slurry and mixed foranother 5 minutes using an overhead stirrer. Handsheets were thenproduced by the method in Example 3. The final basis weight wasapproximately 80 gsm for these handsheets.

Example 8 Preparation of Synthetic Fibers with and without Tether

PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon BicomponentFibers (and mixtures of two or more of the previous) were dispersed inwater in slurry form such that the solids content was about 20%. Insamples containing a tether, MagnaFloc 919 was then added 0.1% by weightas a tethering agent.

Example 9 Process for Preparing Handsheets from Activated Pulp andTethered Synthetic Fibers

800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2(as applicable) was initially provided. The pulp slurry was activatedwith 0.1% by fiber weight polyDADMAC. Separately, synthetic fibers withand with and without tethers were prepared in accordance with Example 8,so that their performance could be compared with the performance of thesamples prepared with the activated pulp and tethered synthetic fibers.Each slurry was mixed for 5 minutes and then combined and mixed foranother 5 minutes using an overhead stirrer. Handsheets were thenproduced by the method in Example 3. The final basis weight wasapproximately 80 gsm for these handsheets.

Example 10 Preparation of Chitosan Solution

CG-10 was added to water to make a 1% by weight slurry of chitosan.Strong acid was added dropwise to the slurry with stirring until thesolution reached a pH of 2.5 and the chitosan was dissolved.

Example 11 Preparation Of Coated Synthetic Fibers With Chitosan

PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon BicomponentFibers (and mixtures of two or more of the previous) were dispersed inwater in slurry form such that the solids content was about 20%. Astrong acid was then added to the slurry to bring the pH below 2.5. Thesolution in Example 10 was added to the synthetic fiber slurry so thatthe chitosan was 1% by weight of the synthetic fibers. The pH was thenraised back to 8-9 with a strong base to precipitate any unboundchitosan.

Example 12 Process for Preparing Handsheets from Pulp andChitosan-Coated Synthetic Fibers

800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2(as applicable) was initially provided. Separately, chitosan-coatedsynthetic fibers were prepared as a slurry in accordance with Example11, where chitosan exemplifies a tethering agent. Each slurrypreparation was mixed for 5 minutes, then samples of the uncoated pulpslurry were combined with the chitosan-coated synthetic fibers slurryand mixed for another 5 minutes using an overhead stirrer. Handsheetswere then produced by the method in Example 3. The final basis weightwas approximately 80 gsm for these handsheets.

Example 13 The Effect of Latex-Coated Starch on Strength andHydrophobicity

Handsheet samples were prepared from activated pulp in accordance withExample 7, where the amount of latex-coated and tether-bearinglatex-coated starch (StaLok 300) was 4.25% of the solids weight. Thelatex-coated starch had been coated with COSEAL 30061A in accordancewith Example 5. The tether-bearing latex-coated starch had been coatedwith COSEAL30061A and then tethered with MagnaFloc 919 in accordancewith Example 6. Control handsheets were also prepared in accordance withExample 3 (no activation) using the latex-coated starch particles ofExample 5 (no tether). Strength data was gathered from handsheet samplesmade with: (1) activated pulp and tether-bearing latex-coated samples(“ATA treated”), (2) activated pulp and non-tether-bearing latex-coatedparticles, and (3) non-activated pulp and non-tether-bearinglatex-coated particles. For ATA-treated samples, the tether used on thestarch was 0.1% MagnaFloc 919 by solids and the activator on the pulpwas 0.1% polyDADMAC by solids. The max load for each sample was measuredusing an Instron as in Example 4. Data were normalized by the mass toshow load contribution per overall solids weight. Graph 1 (FIG. 2) showsthe strength data with all of the aforementioned conditions mentioned inthis example. FIG. 2 shows a graph of normalized max. load examining theeffect of pulp with and without latex-coated starch and with and withoutthe use of ATA treatment. Measurements of the tensile load at failureare comparable between samples showing that the presence of latex hasnot weakened the sheet due to the presence of tethering and anchoringchemistries.

The hydrophobicity improvement with the samples above was also examined.Using handsheet samples prepared as in Example 7, hydrophobicity wastested by depositing a 25 microliter water droplet on the surface of thepaper and recording the time for the droplet to completely absorbed bythe paper. The results of the hydrophobicity tests are shown in Table 1(FIG. 3). FIG. 3 shows a table of normalized water droplet holdoutexamining the effect of pulp with and without latex-coated starch andwith and without the use of ATA. These results demonstrate that the useof the ATA process (and activator-only) to attach latex-coated starch topulp fibers improves the water resistance of the paper by up to 14,500%compared to control samples having no added latex-coated starch.

Example 14 The Effect of Tethered Synthetic Fibers on Strength andHydrophobicity

Samples were prepared as in Example 9, where the amount oftether-bearing synthetic fibers were a total of 15% of the solidsweight. The tether-bearing synthetic fibers had been prepared inaccordance with Example 8. Samples were made both with activator andtether and without either activator or tether. For ATA-treated samples,the tether used on the synthetic fibers was 0.1% MagnaFloc 919 by solidsand the activator on the pulp was 0.1% polyDADMAC by solids. The maxload for each sample was measured using an Instron as in Example 4. Datawere normalized by the mass to show load contribution per overall solidsweight. Graph 2 (FIG. 4) shows the strength data with all of theaforementioned conditions mentioned in this example.

FIG. 4 shows a graph of normalized max. load examining the effect ofpulp with and without synthetic fibers and with and without the use ofATA. Normalized tensile load at failure for the samples show that thereis no significant loss in tensile strength due to inclusion of thesynthetic fibers. The hydrophobicity improvement with the samples abovewas also examined. Using fiber handsheet samples prepared as in Example9, hydrophobicity was tested by depositing a 25 microliter water dropleton the surface of the paper and recording the time for the droplet tocompletely absorbed by the paper. The results of the hydrophobicitytests are shown in Table 2 (FIG. 5). These results demonstrate that theuse of synthetic fibers in combination with pulp fibers improves thewater resistance of the paper by up to 26,600% compared to controlsamples having no added synthetic fibers. FIG. 5 shows a table ofnormalized water droplet holdout examining the effect of pulp with andwithout synthetic fibers and with and without the use of ATA. Waterdroplet holdout times show that there is a >266× gain in droplet holdouttime with the use of polypropylene fibers under several conditions.

Example 15 The Effect of Chitosan-Coated Synthetic Fibers on Strengthand Hydrophobicity

Samples were prepared as in Example 12, where the amount ofchitosan-coated synthetic fibers were a total of 15% of the solidsweight. The chitosan-coated synthetic fibers had been prepared inaccordance with Example 11. The max load for each sample was measuredusing an Instron as in Example 4. Data were normalized by the mass toshow load contribution per overall solids weight. Graph 3 (FIG. 6) showsthe strength data with all of the aforementioned conditions mentioned inthis example. FIG. 6 shows a graph of normalized max. load examining theeffect of pulp with synthetic fibers with and without the use ofchitosan. Normalized tensile load at failure for the samples show thatthere is no significant loss in tensile strength due to inclusion of thesynthetic fibers. The hydrophobicity improvement with the samples abovewas also examined. Using recycled fiber handsheet samples prepared as inExample 12, hydrophobicity was tested by depositing a 25 microliterwater droplet on the surface of the paper and recording the time for thedroplet to completely absorbed by the paper. The results of thehydrophobicity tests are shown in Table 3 (FIG. 7). These resultsdemonstrate that the use of chitosan-coated synthetic fibers improvesthe water resistance of the paper by up to 26,600% compared to controlsamples having no synthetic fibers. FIG. 7 shows a table of normalizedwater droplet holdout examining the effect of pulp with and withoutsynthetic fibers and with and without chitosan coating. Water dropletholdout times show that there is a >266× gain in droplet holdout timewith the use of polypropylene fibers coated with chitosan.

Example 16 Control Virgin Pulp (Softwood Only)

A 0.5% slurry was prepared by blending 93% solids content softwood inwater.

Example 17 Preparation of PCC and Pearl Starch with and without Tether

PCC and Pearl Starch (and mixtures of the two) were dispersed in waterin slurry form such that the solids content was about 20%. In samplescontaining a tether, MagnaFloc 919 was then added 0.05% by weight ofsolids as a tethering agent.

Example 18 Preparation of a Handsheet with PCC and Pearl Starch

600 mL of a 0.5% pulp slurry prepared in accordance with Example 16 wasinitially provided. The pulp slurry was activated with 0.1% by fiberweight polyDADMAC. Separately, starch, PCC, and tethered starch/PCC wereprepared as a slurry in accordance with Example 17. Each slurry wasmixed for 5 minutes and then combined and mixed for another 5 minutesusing an overhead stirrer. Handsheets were then produced by the methodin Example 16. The final basis weight was approximately 60 gsm for thesehandsheets.

Example 19 The Effect of PCC and Pearl Starch on Strength

Samples were prepared as in Example 18, where the amount of PCC, PearlStarch, tether-bearing pearl starch and PCC was between 5% and 30% ofthe solids weight. The tethered PCC with pearl starch had been preparedwith MagnaFloc 919 in accordance with Example 17. Samples were made withboth activator and tether or with neither activator nor tether. ForATA-treated samples, the tether used on the dry-mixed pearl starch andPCC and was 0.05% MagnaFloc 919 by solids and the activator on the pulpwas 0.1% polyDADMAC by solids. The max load for each sample was measuredusing an Instron as in Example 16. Data were normalized by the mass toshow load contribution per overall solids weight. Graph 4 (FIG. 8) showsthe strength data with all of the aforementioned conditions mentioned inthis example. As shown in FIG. 8, the ATA treatment improves retentionand reduces the loss of tensile strength at similar loadings of PCC.

Example 20 Preparation of Iron (III) Oxide with and without Tether

Iron (III) Oxide particles were dispersed in water in slurry form suchthat the solids content was about 20%. In samples containing a tether,MagnaFloc 919 was then added 0.05% by weight of solids as a tetheringagent.

Example 21 Preparation of a Handsheet with Iron (III) Oxide

600 mL of a 0.5% pulp slurry prepared in accordance with Example 16 wasinitially provided. The pulp slurry was activated with 0.1% by fiberweight polyDADMAC. Separately, Iron (III) Oxide with and without tetherwere prepared as a slurry in accordance with Example 20. Each slurry wasmixed for 5 minutes and then combined and mixed for another 5 minutesusing an overhead stirrer. Handsheets were then produced by the methodin Example 16. The final basis weight was approximately 60 gsm for thesehandsheets.

Example 22 Analysis of Magnetization of Iron (III) Oxide Handsheets

1″ by 2″ pieces of handsheets with iron (III) oxide prepared in Example21 were held to a ceramic magnet to verify holdout of Iron (III) Oxidein the sheet. Sheets containing as little as 5% Iron (III) oxide bysolids weight held onto the magnet with no other support.

Example 23 Preparation of Softwood Pulp with Polymer Activator

3.5% solids unrefined softwood pulp was diluted with water to 1% solids.0.1% polyDADMAC by weight of softwood solids was added to the slurry andmixed gently for 30 seconds. The activated slurry was then diluted withwater down to 0.5% solids.

Example 24 Preparation of Hardwood Pulp with Polymer Tether

3.5% solids unrefined hardwood pulp was diluted with water to 1% solids.0.1% MagnaFloc 919 by weight of hardwood solids was added to the slurryand mixed gently for 30 seconds. The tethered slurry was then dilutedwith water down to 0.5% solids.

Example 25 Process for Preparing Handsheets from Activated Softwood andTethered Hardwood Pulp

260 mL each of 0.5% solids activated softwood and tethered hardwood pulpas described in Examples 5 and 6 were combined and mixed for 5 minutes.Handsheets were then produced by the method in Example 3. The finalbasis weight was approximately 80 gsm for these handsheets.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A system for papermaking, comprising: a first population of fibers dispersed in an aqueous solution and complexed with an activator, and a second population of composite additive particles bearing a tethering material, wherein the addition of the second population to the first population attaches the composite additive particles to the fibers by the interaction of the activator and the tethering material.
 2. The system of claim 1, wherein the first population comprises cellulosic fibers.
 3. The system of claim 1, wherein the first population comprises synthetic fibers.
 4. The system of claim 1, wherein the composite additive particles comprise a particle selected from the group of a PCC particle, a TiO2 particle, a magnetic particle, and a silver colloid particle.
 5. The system of claim 1, wherein the composite additive particles comprise a latex component and a starch component.
 6. A method for manufacturing a paper product, comprising: activating a first population of fibers in a liquid medium with an activator, forming a second population of composite additive particles, treating the second population with a tethering material to form tether-bearing composite additive particles, wherein the tethering material is capable of interacting with the activator, adding the second population to the activated population of fibers to form a treated paper matrix, and forming the paper matrix to manufacture the paper product.
 7. The method of claim 6, wherein the first population comprises cellulosic fibers.
 8. The method of claim 6, wherein the first population comprises synthetic fibers.
 9. The method of claim 6, wherein the composite additive particles comprise a particle selected from the group of a PCC particle, a TiO2 particle, a magnetic particle, and a silver colloid particle.
 10. The method of claim 6, wherein the composite additive particles comprise a latex component and a starch component.
 11. A method of manufacturing a paper product, comprising: providing a first population of fibers and a second population of fibers, wherein the fibers have low attachable affinity for each other, activating the first population of fibers in a liquid medium with an activator, treating the second population of fibers with a tethering material to form tether-bearing fibers, wherein the tethering material is capable of interacting with the activator, adding the second population of tether-bearing fibers to the activated population of fibers to form a treated paper matrix, and forming the paper matrix to manufacture the paper product.
 12. The method of claim 11, wherein at least one population of fibers comprises synthetic fibers.
 13. The method of claim 12, wherein at least one population of fibers comprises cellulosic fibers.
 14. The method of claim 11, wherein one of the first population and the second population comprises hardwood fibers, and the other of the first population and the second population comprises softwood fibers.
 15. A fibrous web, comprising: a first population of fibers and a second population of fibers, wherein an activator has been attached to the first population of fibers and a tethering material has been attached to the second population of fibers, the tethering material interacting with the activator to attach the first population of fibers to the second population of fibers as a fibrous web.
 16. A paper product, comprising the fibrous web of claim
 15. 17. The paper product of claim 16, wherein the first population of fibers comprises cellulosic fibers, and the second population of fibers comprises synthetic fibers.
 18. The paper product of claim 17, wherein the first population of fibers consists essentially of cellulosic fibers, and the second population of fibers consists essentially of synthetic fibers.
 19. The paper product of claim 17, wherein the first population of fibers comprises one of softwood fibers or hardwood fibers, and the second population of fibers comprises the other of softwood and hardwood fibers.
 20. The paper product of claim 17, wherein the first population of fibers comprises cellulosic fibers, and the second population of fibers comprises non-cellulosic natural fibers.
 21. A method of forming a fibrous web, comprising: providing a first population of fibers, activating the first population of fibers in a liquid medium with an activator, preparing a population of composite particles, wherein the composite particles comprise a latex component and a starch component, treating the population of composite particles with a tethering material to form tether-bearing composite particles, wherein the tethering material is capable of interacting with the activator to attach the composite particles to the fibers to form particle-bearing fibers, and processing the particle-bearing fibers to gelatinize the starch component and to melt the latex component, thereby distributing the melted latex component through the fibers and binding the fibers together to form the fibrous web.
 22. The method of claim 20, further comprising: providing a second population of fibers, wherein the second population of fibers has low attachable affinity for the first population, activating the second population of fibers with an activator, and adding the second population of fibers to the first population of fibers either before or after the activation step for either population, wherein the population of tether-bearing composite particles attaches to the first population of fibers and the second population of fibers to form particle-bearing fibers, and wherein the processing of the particle-bearing fibers distributes the melted latex component through the first population and the second population of fibers and binds the first population and the second population of fibers together to form the fibrous web.
 23. A paper product formed from the fibrous web of claim
 20. 